High-Z cast reflector compositions and method of manufacture

ABSTRACT

A scintillator pack comprises an array of scintillator pixels and an x-ray absorbing layer disposed in inter-scintillator regions between the scintillator pixels. The x-ray absorbing layer acts to absorb x-rays and protect underlying regions of the inter-scintillator regions. The x-ray absorbing layer may be formed by a number of methods including casting and melt infiltration.

BACKGROUND OF INVENTION

This invention relates generally to high-Z inter-scintillator materialsand a method of manufacturing such inter-scintillator reflectors, wherethe high-Z inter-scintillator material acts as a high density x-rayabsorber.

Solid state detectors for computed tomography (CT) imaging usescintillators to convert x-rays into scintillation radiation whichitself is converted to an electrical signal with a photodiode. Detectorarrays are typically comprised of scintillator pixels separated by aninter-scintillator material used to pipe the scintillation radiationtowards the diode. The materials used as the inter-scintillator materialare typically highly reflecting at the scintillation radiationwavelengths emitted by the scintillator in order to collect a largefraction of the scintillation radiation at the diode.

Appropriate inter-scintillator materials include high refractive indexsolid materials such as TiO₂ formed in a castable low index medium suchas an epoxy.

One drawback of such a system is the darkening of the inter-scintillatormaterial when it is struck by a dose of x-rays commonly used in CTimaging. A typical dose over the life of the detector is 1 Mrad. Thisdarkening results in lower reflectivity and less efficient collection ofthe scintillation radiation, and thus a lowering of the sensitivity ofthe x-ray detector.

Furthermore, the darkening is often not uniform over the entrance faceof the detector. This lack of uniformity in darkening can result inimage degradation if the detector is not properly calibrated. Inaddition to the inter-scintillator material itself, the diode below thereflector is also sensitive to radiation and must be protected from thex-ray beam.

Current CT detectors use a collimator assembly to protect theinter-scintillator material from damage by x-rays. This assemblyconsists of tall tungsten plates aligned perpendicular to the plane ofthe x-ray fan beam. This assembly is primarily used to minimizescattered x-rays from reaching the scintillator, but is also used toprotect the inter-scintillator material between pixels from the x-rays.For multi-slice CT, where the detector is segmented in the directionparallel to the fan beam, wires are used to protect the reflector anddiodes. These wires are strung between the deep plates in groovesmachined in the plates.

The manufacturing of such a two dimensional collimator with plates andwires is complex. The separate construction of the collimator withprotective wires and the scintillator/reflector body requires accuratealignment of these devices during construction of the complete detector.This alignment cannot be done optically since the inter-scintillatormaterial between the scintillator pixels is obscured by reflectormaterial covering the top of the pixels (“surface reflector”).Therefore, either x-ray alignment or rigorous dimensional tolerancesmust be used to ensure that the reflector material is aligned with theprotective wires.

SUMMARY OF INVENTION

In view of the foregoing, it would be desirable to provide ascintillator pack including a scintillator pixel array, and an x-rayabsorbing layer in the inter-scintillator regions that avoids or reducesthe above mentioned problems. The x-ray absorbing layer eliminates therequirement of protective tungsten cross-wires over theinter-scintillator regions. Thus quality and reproducibility areimproved, while costs are reduced.

In accordance with one aspect of the present invention, there isprovided a scintillator pack. The scintillator pack comprises an arrayof scintillator pixels and an x-ray absorbing layer formed ininter-scintillator regions between the scintillator pixels. The x-rayabsorbing layer comprises a high density x-ray absorbing material.

In accordance with another aspect of the present invention there isprovided an x-ray device. The x-ray device comprises an x-ray source, ascintillator pack, and a scintillation radiation detector. Thescintillator pack has an array of scintillator pixels where a pixel ofthe array emits scintillation radiation upon an x-ray from the x-raysource being absorbed by the pixel. The scintillator pack also includesan x-ray absorbing layer, comprising a high density x-ray absorbingmaterial, formed in inter-scintillator regions between the scintillatorpixels. The scintillation radiation detector is optically coupled to thescintillator pack for detecting scintillation radiation.

In accordance with another aspect of the present invention there isprovided an x-ray detection device. The x-ray detection device comprisesa scintillator pack and a scintillation radiation detector. Thescintillator pack has an array of scintillator pixels where a pixel ofthe array emits scintillation radiation upon an x-ray being absorbed bythe pixel. The scintillator pack also includes an x-ray absorbing layer,comprising a high density x-ray absorbing material, formed ininter-scintillator regions between the scintillator pixels. Thescintillation radiation detector is optically coupled to thescintillator pack for detecting scintillation radiation.

In accordance with another aspect of the present invention there isprovided a method of forming a scintillator pack. According to thisaspect of the invention the method comprises providing an array ofscintillator pixels, and forming an x-ray absorbing layer ininter-scintillator regions between the scintillator pixels, where thex-ray absorbing layer is of a high density x-ray absorbing material.

According to this aspect of the invention the x-ray absorbing layer maybe formed by disposing a melted eutectic alloy of a metal into theinter-scintillator regions between the scintillator pixels.

According to this aspect of the invention the x-ray absorbing layer mayalternatively be formed by disposing a glass melt into theinter-scintillator regions between the scintillator pixels, and coolingthe glass melt to form a glass in the inter-scintillator regions.

According to this aspect of the invention the x-ray absorbing layer mayalternatively be formed by providing a high density x-ray absorbingpowder, dispersing the powder within a liquid matrix to form a precursormix, disposing the precursor mix within the inter-scintillator regions,and solidifying the precursor mix to form a solid layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a scintillator pack including an x-rayabsorbing layer according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the scintillator pack of FIG. 1.

FIG. 3 is a stylized perspective of a portion of a CT machine containinga scintillator pack including an x-ray absorbing layer according toanother embodiment of the invention.

FIG. 4 is a schematic of an x-ray detection device according to anotherembodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a scintillator pack 10 according to an embodiment of thepresent invention. The scintillator pack 10 includes an array 12 ofscintillator pixels 12 a, 12 b, 12 c, etc. FIG. 1 shows only a fractionof the scintillator pack for ease of illustration, and in general, thearray 12 will include many more pixels than those shown in FIG. 1. Thescintillator pack 10 further includes inter-scintillator regions 14 a,14 b, 14 c, etc., which are the regions between the scintillator pixels.

The inter-scintillator regions 14 a, 14 b, 14 c, etc. are filled with anx-ray absorbing layer 16.

The x-ray absorbing layer 16 comprises a high density x-ray absorbingmaterial. In application, the x-ray absorbing material preferably shouldbe able to absorb x-rays in application within an effective thickness ofabout 3 mm. The x-rays are considered to be sufficiently absorbed if thethickness stopsat least 99% of the x-rays. In this regard, the highdensity x-ray absorbing material should have a high effective atomicnumber (Z). The x-ray stopping power of a material is primarilydependent on the effective atomic number of the material. Combined withthe mass density, the atomic number (Z) determines the electroncross-section which interacts with the x-ray radiation. Specifically,the ratio of the intensity of the x-ray radiation transmitted through amaterial, I, to the x-ray radiation incident upon a material, I₀, isgiven as I/I₀=exp{−(μ/ρ)x}, where μ is the absorption coefficient whichis proportional to Z², ρ is the mass density, and x is the distancetraveled through the material.

In application, the x-rays will impinge upon the scintillator pack at anangle that is approximately normal to the top surface. Thus, a largefraction of the x-rays impinging upon the inter-scintillator regions ofscintillator pack should preferably be stopped within a distance ofabout 3 mm upon traveling in the x-ray absorbing layer 16. Beneficially,the inter-scintillator regions below this first 3 microns will belargely protected from x-rays.

The x-ray absorbing layer 16 should also not substantially absorbscintillation radiation from the adjacent pixels. Instead, it ispreferred that the x-ray absorbing layer 16 be highly reflecting toscintillation radiation so that the x-ray absorbing layer 16 acts tochannel scintillation radiation in the pixels to an underlyingscintillation radiation detector (not shown in FIG. 1). In this regard,it is preferred that the x-ray absorbing layer 16 have an index ofrefraction greater than 1.80.

The scintillator pack may also include a scintillation radiationreflecting layer 18 which extends over the top of the scintillatorpixels. The scintillation radiation reflecting layer 18 acts to reflectscintillation radiation, emitted from a scintillator pixel upon an x-raybeing absorbed by the scintillator material in the pixel, back down toan underlying scintillation radiation detector. Thus, the scintillationradiation reflecting layer 18 is made of an appropriate scintillationradiation reflecting material. Optionally, the scintillation radiationreflecting layer 18 may be excluded.

In FIG. 1 the scintillation radiation reflecting layer 18 is formeddirectly on the top of the scintillator pixels. However, it may bedesirable to include one or more layers between the scintillationradiation reflecting layer 18 and the scintillator pixels. For example,depending on the scintillation radiation reflecting layer 18, thematerial of the scintillator pixels, and the method of depositing thescintillation radiation reflecting layer 18, it may be desirable toinclude an adhesion or nucleation layer or layers between thescintillator pixels and the scintillation radiation reflecting layer 18.

FIG. 2 shows a cross-sectional view of the scintillator pack of FIG. 1along the line a—a. In FIG. 2, the array 12 is a two-dimensional arraywith an x-ray absorbing layer 16 in the inter- scintillator regionsbetween the pixels 12 a 1, 12 a 2, 12 b 1, 12 b 2, 12 c 1, 12 c 2 of thearray 12. In FIG. 2, the two-dimensional array contains rectangularcross-sectioned scintillator pixels with the x-ray absorbing materialforming a grid pattern. However, the pixels may be arranged such thatthe x-ray absorbing material forms a pattern other than a grid pattern.The pixels may have a cross-section other than rectangular, such ascircular or triangular. The array need not be two-dimensional and mayinstead be one-dimensional.

The scintillator material of the scintillator pixels may be anyappropriate x-ray scintillator material. Appropriate scintillator hostmaterials include, for example, gadolinium gallium garnet, gadoliniumscandium gallium garnet, gadolinium scandium aluminum garnet, lutetiumaluminum garnet, ytrrium gallium garnet, ytrrium gadolinium oxide,Gd₂O₂S, CsI:Tl, CsI, and lutetium orthosilicate.

The scintillation radiation reflecting material will depend upon thewavelength of the scintillation radiation emitted by the scintillator.For example, in the case of visible scintillation radiation, thescintillation radiation reflecting material could be a high refractiveindex solid such as TiO₂ in a castable low index medium such as anepoxy. Silver and gold plated pressure sensitive adhesives andmultilayer dielectric stacks can also be used as scintillation lightreflectors.

The high density x-ray absorbing layer comprises a high density materialwith good x-ray absorbing properties. Examples of preferred high densitymaterials include high density metals such as hafnium, tantalum,gadolinium, lutetium, bismuth, antimony, lead, cadmium, tungsten,molybdenum, niobium, platinum, palladium, silver, and alloys of thesemetals. The high density material need not be in elemental form, and maybe a compound such an oxide, sulfate, sulfide, or fluoride, for example.Preferred oxides include high density compounds, such as hafnium oxide,tantalum oxide, gadolinium oxide, lutetium oxide, tungsten oxide, leadoxide, bismuth titanium oxide, barium titanium oxide, barium hafniumoxide, etc.

The x-ray absorbing layer 16 may comprise only high density x-rayabsorbing material. Alternatively, the x-ray absorbing layer may be acomposite material which comprises both high density x-ray absorbingmaterials and other materials. In any case, the composite materialshould have good x-ray absorbing properties. For example, the x-rayabsorbing layer may be a composite material including a polymer organicor inorganic binder with high density particles embedded within theorganic or inorganic binder. Appropriate organics include, for example,epoxy, polyester, and polymethylmethacrylate. Inorganic binders includesilicates or phosphates, such as potassium silicate and aluminumphosphate, respectively. The x-ray absorbing material would then be abinder matrix filled with high density particles.

The high density particles preferably include high density materialsdiscussed above. For example, the high density particles may be hafnium,tantalum, gadolinium, lutetium, bismuth, antimony, lead, cadmium,tungsten, molybdenum, niobium, platinum, palladium, silver, and alloysof these metals. The high density particles may also include compoundssuch as oxides, sulfates, sulfides, and fluorides. For example,preferred oxides for the high density particles include compounds, suchas hafnium oxide, tantalum oxide, gadolinium oxide, lutetium oxide,tungsten oxide, and lead oxide. Appropriate sulfates include gadoliniumsulfate and barium sulfate, for example. Other appropriate high densitycompounds include bismuth titanate, barium titanate, and barium hafnate.

The concentration of the high density particles in the x-ray absorbinglayer 16 will depend upon the composition of the high density particleschosen, and the x-ray energy to be used in operation for thescintillator pack 10. The ratio of the intensity of the x-ray radiationtransmitted through a material, I, to the x-ray radiation incident upona material, I₀, is given as I/I₀=exp{−(μ/ρ)x}, where μ is the absorptioncoefficient which is proportional to Z², and dependent upon the x-rayenergy, and ρ is the mass density, and x is the distance traveledthrough the material. In general, high density particles, i.e.,particles with a greater atomic number, will provide greater stoppingpower in attenuating incident x-rays. Thus, a lower concentration ofhigh density particles may be sufficient in the case that particles witha particularly high density are used. Also, in general, theconcentration of high density particles in the x-ray absorbing layer 16should be greater for higher energy x-rays than for lower energy x-rays.The concentration of the high density particles should be sufficient tostop x-rays within an effective distance of about 3 mm.

The average size of the particles chosen will depend, in part, on thedesired light scattering quality of the x-ray absorbing layer. Becausethe light scattering due to the particles is wavelength dependent, theaverage size chosen will depend upon the wavelength of the scintillationradiation. For typical scintillation radiation wavelengths the size ofthe particles is preferably within the range of about 0.15 to the about0.35 microns.

The x-ray absorbing material may be a glass or crystalline material, ora material with some other type of structure, or a combined structure.For example, the x-ray absorbing material may be high density glassceramic with embedded crystallites. Appropriate glasses for the highdensity glass ceramic include fluoride glasses such as HBLAN (hafniumbarium lanthanum aluminum sodium fluoride), ZBLAN (zirconium bariumaluminum sodium fluoride), rare earth borates, bismuth borosilicates,aluminates, tantalates and tungstates. The crystallites in the glassmatrix may be of the same material as the matrix or of a differentmaterial. For example, if the glass matrix comprises HBLAN, thecrystallites may be HBLAN crystallites precipitated within the glassmatrix. Preferably, the size of the crystallites is within the range ofabout 0.15 to the about 0.35 microns so that the crystallites act asgood light scattering agents for typical scintillation radiationwavelengths. Alternatively, if the x-ray absorbing layer comprises ahigh density glass with sufficient scintillation radiation reflectionfor a particular application, the glass need not include crystallites.

In use, each scintillator pixel of the scintillator pack is opticallycoupled to a photodetector (not shown in FIGS. 1 and 2), such as aphotodiode. Each scintillator pixel may be coupled to its correspondingphotodetector simply by placing the bottom of the scintillator pixeladjacent to its corresponding photodetector. Alternatively, thescintillation light might be piped from the scintillator pixel to itscorresponding photodetector via a fiber optic or by other means.

A CT scanning system 100 is illustrated schematically in FIG. 3. This CTscanning system 100 comprises a cylindrical enclosure 110 in which thepatient or object to be scanned is positioned. A gantry 112 surroundsthe cylinder 110 and is configured for rotation about the cylinder'saxis. The gantry 112 may be designed to revolve for one full revolutionand then return or may be designed for continuous rotation, depending onthe system used to connect the electronics on the gantry to the rest ofthe system. The electronics on the gantry include an x-ray source 114which preferably produces a fan shaped x-ray beam which encompasses ascintillation radiation detector system 116 mounted on the gantry on theopposite side of the cylinder 110. The fan pattern of the x-ray sourceis disposed in the plane defined by the x-ray source and thescintillation radiation detector system 116.

The scintillation radiation detector system 116 is very narrow or thinin the direction perpendicular to the plane of the x-ray fan beam. Eachpixel 118 of the scintillation radiation detector system incorporates asolid translucent bar of a scintillator material and a photodetectordiode optically coupled to that scintillator bar. The pixels arearranged in an array such as discussed above with respect to FIG. 1. Thepixel array is part of a scintillator pack with an x-ray absorbing layerin the inter-scintillator regions as described above with respect toFIG. 1.

The output from each photodetector diode is connected to an operationalamplifier (not shown) which is mounted on the gantry. The output fromeach operational amplifier is connected either by individual wires 120or by other electronics to the main control system 150 for the CT system100. In the illustrated embodiment, power for the x-ray source andsignals from the scintillation radiation detector are carried to themain control system 150 by a cable 130. The use of the cable 130generally limits the gantry to a single full revolution before returningto its original position.

Alternatively, slip rings or optical or radio transmission may be usedto connect the gantry electronics to the main control system 150 wherecontinuous rotation of the gantry is desired. In CT scanning systems ofthis type, the scintillator material is used to convert incident x-raysto luminescent light which is detected by the photodetector diode andthereby converted to an electrical signal as a means of converting theincident x-rays to electrical signals which may be processed for imageextraction and other purposes.

FIG. 4 is a schematic of an x-ray detection device according to anotherembodiment of the invention. The x-ray detection device includes ascintillator pack 10, such as the scintillator pack discussed supra withrespect to FIG. 1. The scintillator pack 10 includes an array ofscintillator pixels 12 a, 12 b, 12 c, etc., inter-scintillator regions14 a, 14 b, 14 c, etc., an x-ray absorbing layer 16, and a scintillationradiation reflecting layer 18, as also discussed supra. Each of thescintillator pixels 12 a, 12 b, 12 c, is optically coupled to acorresponding cell 30 a, 30 b, 30 c of scintillation radiation detector30. The scintillation radiation detector 30 is shown with only threecells 30 a, 30 b, 30 c for the sake of illustration. In practice, thescintillation radiation detector 30 is not limited to three cells.Typically, the scintillation radiation detector 30 comprises many morecells.

The scintillation radiation detector cells may be, for instance,photodiodes. The output signals of the scintillation radiation detectorcells are coupled to a controller 34 by means of individual wires orother electronics 32.

Methods of forming the scintillator pack of the present invention arenow described. Initially, an array of scintillator pixels is provided,as is known in the art. For example, the scintillator pixels may beformed of bulk polycrystalline scintillator material formed from apowder as disclosed, for example, in U.S. Pat. Nos. 4,473,513,4,518,546, 4,769,353, and 5,521,387. However, the present invention isnot limited to bulk polycrystalline scintillator material and otherscintillator material may also be used.

Once the array of scintillator pixels is provided, the x-ray absorbinglayer comprising a high density x-ray absorbing material is then formedin the inter-scintillator regions between the scintillator pixels. Thex-ray absorbing layer may be formed by a number of methods.

According to one embodiment of the invention, the x-ray absorbing layermay be formed by melting a eutetic alloy of a metal, and disposing themelted metal into the inter-scintillator regions between thescintillator pixels. In this embodiment it is preferred that the metalhave good scintillation radiation reflecting properties to channelscintillation radiation towards a photodetector. Appropriate metalsinclude, for example, lead, tungsten, molybdenum, platinum, palladium,bismuth, tin, silver, and alloys thereof. The selected metal or alloysthereof can be impregnated in molten form into the inter-scintillatorregions and then cooled to solidify to form a solid film. Alternately,the metal or alloy can be inserted into the inter-scintillator regionsin non-molten form and then heated to melt and bond the metal or alloyto the surface of the scintillator pixels defining the boundaries of theinter-scintillator regions. As an alternative method the metal or alloymay be introduced into the inter-scintillator regions by evaporation orelectrodeposition.

According to another embodiment of the invention, the x-ray absorbinglayer may be formed by disposing a high density glass melt into theinter-scintillator regions. For example, the components of HBLAN orZBLAN glass may be heated to form a glass melt and then melt infiltratedinto the inter-scintillator regions. The molten glass is poured intointer-scintillator regions. The melt is then cooled to form a glass inthe inter-scintillator regions.

If desired, the high density glass may then be further annealed at atemperature and atmosphere sufficient to form crystallites of theceramic within the glass matrix, and thus form a high density glassceramic. The process of recrystallization of the glass can be performedat a predetermined temperature regime below the melting point of theparent glass—usually around ⅓ to ½ the melting point. Thetemperature/time profile and the atmosphere for recrystallization isdependent upon the particular glass composition. For example, a bismuthtitanate phase can be recrystallized from a Bismuth titanium borateglass at ˜400° C. in air. Beneficially, the crystallites act asscattering centers for the scintillation radiation. In this regard it ispreferable that the size of the particles be within the range of about0.15 to 0.35 microns for typical scintillation radiation wavelengths.

According to another embodiment of the invention, the x-ray absorbinglayer may be formed by casting. In this embodiment, a high density x-rayabsorbing powder is provided. The powder may be, for example, a highdensity metal or a high density metal compound. Appropriate high densitymetal compounds include oxides, sulfates, sulfides, fluorides andcombinations of these compounds. Appropriate oxides include hafniumoxide, tantalum oxide, gadolinium oxide, lutetium oxide, tungsten oxide,and compounds thereof such as barium hafnate, bismuth titanate, lutetiumhafnate etc.

The powders with the required particle sizes may be produced by any ofnumber of techniques known in the art. For example, the powders may beproduced by the reaction of oxides or oxide precursors through a heattreatment step followed by comminution and classification to therequired particle size range. The powders may also be produced byprecipitation and heat treatment of the precipitate from appropriateprecursor solutions followed by comminution and classification asneeded. The powders may also be produced by hydrothermal synthesis fromsuitable precursors, synthesis through a molten salt process, and byother known processes such as flame pyrolysis, self propagatedsynthesis, and evaporative reactive calcining. Preferably, the size ofthe particles is within the range of about 0.15 to 0.35 microns.

The high density powder is then dispersed within a liquid matrix to forma precursor mix, such as a slurry. The liquid matrix may be, forexample, suitable polymeric organic or inorganic binders, such as epoxy,polystyrene, polyester, acrylate, silicates and phosphates.Additionally, additives may be added to the precursor mix to stabilizethe precursor mix to x-ray radiation and thus prevent discoloration.Examples of such additives include TMBOX, hexahydro-4-methylphthalicanhydride, and cerium salts.

The precursor mix is then cast within the inter-scintillator regions.For example, the slurry may be impregnated into the inter-scintillatorregions under pressure or vacuum. The cast precursor mix is thensolidified to form a solid layer. The method of solidifying the castprecursor mix will depend upon the composition of the mix. For example,the slurry may be solidified through a heat treatment step during whichthe binder polymerizes into a solid containing the filler particlesuniformly dispersed in its matrix. If the mix contains epoxy as abinder, the mix may be heat treated at the required temperature over aspecific period of time to polymerize the binder into a solid. Thesetreatments beneficially may increase the resistance of the x-rayabsorption layer to water vapor.

EXAMPLE

One example of a high density x-ray absorbing material according to theinvention was formed as follows. A slurry containing barium hafnatepowder in Epotek 301 binder was prepared by dispersing the powder in apart of the binder resin. This was accomplished by mixing the powder andthe binder in ajar. The volume fraction of the powder in the slurry thusformed was 12.5%. The mixed slurry was then de-aired in a vacuumdesiccator and a hardener was added to the mix. The slurry was then castbetween two scintillator plates separated with a gap of about 0.08 mm.The cast plate assembly was then heat treated at 60° C. for 16 hours toensure complete curing, i.e., polymerization of the slurry. Theresulting high density reflector layer had a reflectance of 82% at 610nm.

The preferred embodiments have been set forth herein for the purpose ofillustration. However, this description should not be deemed to be alimitation on the scope of the invention. Accordingly, variousmodifications, adaptations, and alternatives may occur to one skilled inthe art without departing from the spirit and scope of the claimedinventive concept.

All of the patents which are mentioned above are incorporated herein byreference.

What is claimed is:
 1. A scintillator pack comprising: an array ofscintillator pixels; and x-ray absorbing regions surrounding thescintillator pixels, the x-ray absorbing regions being filled with ahigh density x-ray absorbing material that consists essentially of ahigh density glass ceramic selected from the group consisting of hafniumbarium lanthanum aluminum sodium fluoride, zirconium barium aluminumsodium fluoride, rare-earth borates, bismuth borosilicates, aluminates,tantalates, and tungstates.
 2. A scintillator pack comprising: an arrayof scintillator pixels; and x-ray absorbing layer comprising a highdensity x-ray absorbing material, the x-ray absorbing layer being formedin inter-scintillator regions between the scintillator pixels, whereinthe high density x-ray absorbing material comprises a high density glassceramic.
 3. The scintillator pack of claim 2, wherein the high densityglass ceramic comprises crystallites embedded within a glass.
 4. Thescintillator pack of claims 3, wherein the crystallites have an averagesize in the range of about 0.15 microns to about 0.35 microns.
 5. Thescintillator pack of claim 3, wherein the glass is a heavy metalfluoride glass.
 6. The scintillator pack of claim 5, wherein the heavymetal fluoride glass is one of HBLAN (hafnium barium lanthanum aluminumsodium fluoride) and ZBLAN (zirconium barium lanthanum aluminum sodiumfluoride).
 7. A method of forming a scintillator pack comprising thesteps of: providing an array of scintillator pixels; filling regionssurrounding the pixels with a high density x-ray absorbing material thatconsists essentially of a melted glass ceramic; and cooling the meltedglass ceramic to form a glass ceramic in said regions.
 8. A method offorming a scintillator pack comprising the steps of: providing an arrayof scintillator pixels; and forming an x-ray absorbing layer comprisinga high density x-ray absorbing material inter-scintillator regionsbetween the scintillator pixels; wherein the step of forming an x-rayabsorbing layer comprises disposing a glass melt into theinter-scintillator regions between the scintillator pixels, cooling theglass melt to form a glass in the inter-scintillator regions, andannealing the glass at a sufficient temperature to precipitatecrystallites within the glass.
 9. The method of forming a scintillatorpack according to claim 8, wherein the glass is one of HBLAN (hafniumbarium lanthanum aluminum sodium fluoride), ZBLAN (zirconium bariumlanthanum aluminum sodium fluoride), rare earth borates, bismuthborosilicates, aluminates, tantalates, and tungstates.
 10. A method offorming a scintillator pack comprising the steps of: providing an arrayof scintillator pixels; forming an x-ray absorbing layer comprising ahigh density x-ray absorbing material in inter-scintillator regionsbetween the scintillator pixels, wherein the step of forming the x-rayabsorbing layer comprises the steps of: providing a high density x-rayabsorbing powder; dispersing the powder within a liquid matrix to form aprecursor mix; disposing the precursor mix within the inter-scintillatorregions; and solidifying the precursor mix to form a solid layer,wherein the step of solidifying the precursor mix comprises annealingthe precursor mix.
 11. A method of forming a scintillator packcomprising the steps of: providing an array of scintillator pixels;forming an x-ray absorbing layer comprising a high density x-rayabsorbing material in inter-scintillator regions between thescintillator pixels, wherein the step of forming the x-ray absorbinglayer comprises the steps of: providing a high density x-ray absorbingpowder; dispersing the powder within a liquid matrix to form a precursormix; disposing the precursor mix within the inter-scintillator regions;and solidifying the precursor mix to form a solid layer, wherein thestep of solidifying the precursor mix comprises treating the precursormix with electromagnetic radiation.
 12. The method of forming ascintillator pack according to claim 11, wherein the electromagneticradiation is selected from the group consisting of x radiation andultraviolet radiation.
 13. A method of forming a scintillator packcomprising the steps of: providing an array of scintillator pixels;forming an x-ray absorbing layer comprising a high density x-rayabsorbing material in inter-scintillator regions between thescintillator pixels, wherein the step of forming the x-ray absorbinglayer comprises the steps of: providing a high density x-ray absorbingpowder; dispersing the powder within a liquid matrix to form a precursormix; disposing the precursor mix within the inter-scintillator regions;and solidifying the precursor mix to form a solid layer, wherein thestep of solidifying the precursor mix comprises polymerizing theprecursor mix.
 14. A method of forming a scintillator pack comprisingthe steps of: providing an array of scintillator pixels; forming anx-ray absorbing layer comprising a high density x-ray absorbing materialin inter-scintillator regions between the scintillator pixels, whereinthe step of forming the x-ray absorbing layer comprises the steps of:providing a high density x-ray absorbing powder; dispersing the powderand an additive within a liquid matrix to form a precursor mix, theadditive preventing discolorization of the x-ray absorbing layer;disposing the precursor mix within the inter-scintillator regions; andsolidifying the precursor mix to form a solid layer.